硅酸盐水泥的初凝时间不得早于45分钟，终凝时间不得迟于390分钟。
The initial setting time of Portland cement shall not be earlier than 45 minutes, final set time not later than 390 minutes.
产生原因：振捣后没有用拖板、刮尺抹平；混凝土未达终凝就在上面行人和操作。
Reasons: No scraping work after vibration; People walks or works on concrete before final set.
指出了商品砼的优点，详细分析了砼终凝前和砼终凝后出现裂缝的原因，并提出相应的控制措施。
The article points out the advantage of commercial concrete, expounds the cause of the crack before and after concrete coagulation, and presents the corresponding control measures.
结果表明：（1）高钙灰的掺入改善了胶砂的工作性，降低了标准稠度用水量，延缓了胶材的初终凝时间；
The results show: (1) with high calcium mixing, concrete workability was modified, the water quantity needed for standard consistence decreased, initial and final setting time increased;
半水石膏凝结硬化很快，其初终凝时间为6 ~30分钟，可操作时间只有5 ~10分钟，往往不能满足石膏基材料的成型与施工的需要。
Setting time of gypsum plaster is very short, usually only 6 ~ 30 min, and operation time is only 5-10 min, which cannot satisfy the practical plastering and construction of gypsum-based material.
半水石膏凝结硬化很快，其初终凝时间为6 ~30分钟，可操作时间只有5 ~10分钟，往往不能满足石膏基材料的成型与施工的需要。
Setting time of gypsum plaster is very short, usually only 6 ~ 30 min, and operation time is only 5-10 min, which cannot satisfy the practical plastering and construction of gypsum-based material.
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